In many electrical installations, systems for uninterruptible electrical power supply (UPS) are used to ensure the operation of the electrical installations regardless of malfunctions in the energy supply network. A UPS is used to provide an auxiliary energy supply in the event of a malfunction of the normal energy supply. UPS is therefore also referred to below using the term “auxiliary electrical power supply”.
For auxiliary electrical power supply, accumulators are typically used which are connected to an auxiliary electrical power supply device and alternatively supply a load which is connected to the auxiliary electrical power supply with electrical energy. An accumulator is a store for electrical energy, typically based on an electrochemical system which comprises one or more secondary cells which can be connected in series in order to increase the overall voltage or which can be connected in parallel in order to increase the capacity. The term “battery” is used below to refer to rechargeable batteries and is consequently used synonymously with accumulators.
During normal operation of the energy distribution network, electrical energy is supplied by the auxiliary electrical power supply device both to the connected load and to the battery. In the event of a malfunction in the energy supply network, the battery begins to discharge towards the load whose electrical energy supply is consequently not interrupted. When the energy distribution network returns to its normal operation, a supply of electrical energy is again provided both to the load and to the battery.
In installations with uninterruptible power supplies (UPS) with high expectations with regard to availability, the battery of the UPS is the element which decisively determines the possible duration of the battery operation, i.e., the possible buffer time and the service life of the installation and consequently the availability.
The battery management of a UPS therefore assumes great significance. A battery which is handled correctly in accordance with its type substantially increases the availability of the installation. A significant element of the battery management is the charging unit which can contribute significantly to maintaining the quality of the battery.
In order to be able to make best use of the capacity of a battery, the end-of-charge voltage is set to the highest possible level. A large amount of energy is thus stored in the battery. On the other hand, in order to maximise the service life of a battery, a somewhat smaller end-of-charge voltage can be used. In this manner, however, the capacity of the battery is not quite fully exploited in favour of the longer service life.
Therefore, the relationship between the service life of the battery and the possible buffer time can be established with a precisely defined end-of-charge voltage. The necessary end-of-charge voltage changes with the temperature of the battery. A UPS which takes into consideration the battery temperature during charging preserves the battery and maximises the service life of the battery and the possible buffer time.
DE 198 34 740 A1 describes a battery which has an integrated monitoring device in order to achieve a long service life and a good current discharge capacity, with various operating states of the battery being detected, stored and compared with stored values by means of sensors and indications regarding the charging state and the general technical state of the battery being derived therefrom.
In industrial UPSs, the auxiliary electrical power supply device which contains the electronic system of the UPS is typically located in a housing which is mounted, for example, on a top-hat rail, but the battery may be mounted remotely at a different location. Values for the battery voltage measured by the auxiliary electrical power supply device deviate from the actual battery voltage owing to the voltage drop on the line between the battery and the UPS. A temperature which is measured by the auxiliary electrical power supply device, for example, by means of a sensor arranged in the electronic system, may also deviate from the actual battery temperature.
Those deviations typically cannot be corrected by the auxiliary electrical power supply device so that the battery is not optimally charged.